1. Field of the Invention
The present invention pertains to apparatus and method for producing exhaust flow, for providing thrust, for example. More particularly, the present invention relates to techniques for producing thrust for propulsive purposes, such as by rocket engines, and finds particular application in the field of engines for space travel.
2. Brief Description of the Prior Art
In general, the thrust provided by a rocket is directly proportional to both the exhaust mass flow rate of the rocket plume and the temperature of the plume. The specific impulse is directly proportional to the velocity of the exhaust particles, which in turn is also proportional to the plume temperature. High specific impulse is consistent with efficient propulsion. The desired high temperature, however, is limited by the temperature limits of the materials of which the rocket is constructed and, in the case of chemical rockets, to temperatures characteristic of chemical reactions. Presently, rockets achieve high thrust mainly due to a large mass flow rate rather than high temperature. Such devices are heavy and, because they must carry large quantities of fuel, cannot burn very long. Plasma thrusters, on the other hand, achieve very high temperatures, that is, their exhaust particles achieve very high velocities. However, their mass flow rates are generally low, thereby limiting the thrust available. Furthermore, the temperature of a plasma exhaust is still limited by the material used to construct a nozzle for directing the plasma exhaust.
It is highly desirable and advantageous to provide a thruster which can generate and expel a plume whose temperature is not limited by the material of the exhaust nozzle, for example, and which would also produce a high mass flow rate. Further, it would be desirable and advantageous to provide such a thruster whose plume mass flow rate and temperature are selectively adjustable so that the resulting plume velocity may be maintained as close as possible to the speed of the vehicle being propelled by the thruster to maximize the propulsive efficiency, that is, the measure of the efficiency of using available thrust.
Gas layers have been used as fuel injection in plasma confinement devices. In such cases, relatively small amounts of gas have been so utilized to avoid quenching of the plasma. The present invention employs a cool gas layer within the exhaust nozzle of a plasma engine to establish a hybrid plume, that is, a plume wherein the fluid properties exhibit drastic variation from one radial position to another.